When operating internal combustion engines, particularly fuel injected internal combustion engines such as those of the diesel type, in certain mining and fuel loading and unloading operations, the possibility of a combustible air/fuel mixture surrounding the engine. In this situation, the air intake to the internal combustion engine may contain enough fuel vapors to provide an uncontrollable air/fuel mixture being fed into the engine solely through the air intake. In such a case, the engine can be caused to overspeed or run away since it is no longer under the control of the fuel input throttle mechanism.
In the prior art, this type of dangerous situation has been guarded against by the provision on the vehicle containing the fuel injected internal combustion engine, of manual shut off controls to shut off either the air or fuel supply or both to the internal combustion engine. Representative examples of such manual control systems are illustrated in U.S. Pat. No. 2,714,290 to Rachuig.
Somewhat more elaborate semi-automatic control systems for controlling an overspeed or engine runaway in a combustible atmosphere are provided in U.S. Pat. No. 2,783,753 to Hofer. In this latter more nearly automatic system, engine manifold pressure sensing devices are used to control air cutoff valves in the air intake system of the engine.
To provide the desired safeguard, an engine overspeed control system should exhibit rapid response time. Furthermore, the overspeed control system should include the capability for testing the operability of the system without actually running the engine in overspeed condition, and of resetting the control system once the engine overspeed condition has ceased.